The long-term goals of this proposal are to elucidate the role and regulation of chemokines and chemokine receptors (CKR) that are involved in the intrathymic migration and maturation of hematopoietic progenitor cells (HSPC)/thymocytes, in normal and HIV-1 infected thymus organs. The thymus has 4 distinct regions where progenitor cells and thymocytes at distinct maturation stages reside. HSPC home to the thymus and migrate from the subcapsular region to the cortex, cortical-medullary junction (CMJ), and to the medulla as they mature. The mechanism of thymocyte migration during maturation in the thymus is not clear. Multiple chemokines (SDF-1, TECK, MDC, IP-10, and ELC) and corresponding CKR (CXCR4, CCR9, CCR4, CXCR3 and CCR7) are expressed in the thymus. We recently discovered that HIV-1 infection of the thymus (or gpl20 interaction with CD4 and CXCR4 or CCR5) led to induction of IP-10 (a ligand of CXCR3). We hypothesize that specific chemokines in specific regions of the thymus are involved in the specific thymocyte migration and maturation. We have recently developed a novel genetic system to inhibit expression and function of CKR with a specific chemokine fused to the HIV-1 Vpu domain that traps and degrades the CKR in the ER (degrakines). We propose to optimize the degrakine system to define and characterize the CKR on HSPC/thymocyte cells that are required for their migration and maturation in the thymus. The findings will shed light on our understanding of the thymus function and of HIV-1 pathogenesis in the thymus. Specifically, we will develop a novel genetic system to define CKR involved in thymocyte migration and maturation in the thymus. By the end of the project, we will 1) create novel "Degrakines" that target most or all of the CKR with known CK ligands expressed in the thymus. 2) We will define the functions of CXCR3, CXCR4, CCR4, CCR7 and CCR9 in thymocyte migration and maturation in the human thymus. Therefore, findings from this highly novel (both in concept and technology) R21-project will open new avenues in understanding the biology of CK/CKR in the thymus, as well as in furthering our understanding of HIV- 1 pathogenesis in the thymus. The parental RO1 grant (AI41356) proposed to 1) define the HIV-1 pathogenic factors which induce thymocyte depletion in the human thymus and 2) determine the mechanisms of the "pathogenic factors" mediating thymus depletion. In addition to the IP-10 and CXCR3 functions implicated in HIV-1 pathogenesis in the thymus, the degrakines will be useful for the study of HIV- 1 pathogenesis in the thymus to capitalize on the novel genetic system and to augment the value of the parental grant.